Method of manufacturing a structure of via hole of electrical circuit board

ABSTRACT

A structure of via hole of electrical circuit board includes an adhesive layer and a conductor layer that are formed after wiring is formed on a carrier board. At least one through hole extends in a vertical direction through the carrier board, the wiring, the adhesive layer, and the conductor layer and forms a hole wall surface. The conductor layer shows a height difference with respect to an exposed zone of the circuit trace in the vertical direction. A conductive cover section covers the conductor layer and the hole wall surface of the through hole. The carrier board is a single-sided board, a double-sided board, a multi-layered board, or a combination thereof, and the single-sided board, the double-sided board, and multi-layered board can be flexible boards, rigid boards, or composite boards combining flexible and rigid boards.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 13/548,345 filedon Jul. 13, 2012, now abandoned entitled “STRUCTURE OF VIA HOLE OFELECTRICAL CIRCUIT BOARD”, currently pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of via hole of electricalcircuit board, and in particular to a structure of via hole ofelectrical circuit board and a manufacturing method thereof.

2. The Related Arts

A printed circuit board (PCB) is a vital electronic component and isalso a support for electronic devices and parts, serving as a providerof connection of wiring of electronic parts. A conventional circuitboard applies a process of printing etching resist to make wiring andpatterns of circuit and is thus referred to as a printed circuit boardor a printed wiring board. Since electronic products are getting smallerand more elaborate, most of the modern-day circuit boards are made bymeans of attaching resist (laminating or coating), and are thensubjected to exposure and development, followed by etching to completethe manufacture of a circuit board.

A process conventionally adopted to make a via hole in a circuit boardis to first provide a carrier board having upper and lower copper foillayers and adhesive layers. A drilling operation is then performed and aconductive cover portion is electroplated. Afterwards, the carrier boardis subjected to coating of dry film, exposure, development, and etchingto form a plurality of etched areas. Finally, laminating is applied tothe etched carried board.

However, the conventional process of making via hole in circuit board isa process that first performs drilling and electroplating and etching isthereafter performed. The flow of operation is simple, but often suffersthe following shortcomings. (1) The thickness of the carrier boardbecome inhomogeneous and this leads to poor yield rate of fine wiringprocess. (2) Impurity may be generated in the process of electroplatingand this leads to reduced yield rate of image transfer and etchingoperation. (3) Size stability of the carrier board deteriorates and thisleads to imprecise alignment for exposure. (4) The structure of thecarrier is changed and this easily leads to poor flexibility.Consequently, further improvement can be made on the known process ofmaking structure of via hole in circuit board.

SUMMARY OF THE INVENTION

In view of the above, the primary object of the present invention is toprovide a structure of via hole of electrical circuit board and amanufacturing method thereof.

A via hole structure adopted by the present invention to handle thetechnical issue of the prior art techniques is that a circuit trace isfirst formed on a carrier board and an adhesive layer and a conductorlayer are subsequently formed. At least one through hole extends in avertical direction through the carrier board, the circuit trace, theadhesive layer, and the conductor layer, and forms a hole wall surface.The conductor layer shows a height difference with respect to an exposedzone of the circuit trace in the vertical direction. A conductive coversection covers the conductor layer and the hole wall surface of thethrough hole. The carrier board can be a single-sided board, adouble-sided board, a multi-layered board, or a combination thereof, andthe single-sided board, the double-sided board, and multi-layered boardcan be circuit boards of different properties, such as flexible boards,rigid boards, or composite boards combining flexible and rigid boards.

Compared with the conventional manufacture process of via hole ofelectrical circuit board, the present invention has the followingadvantages. (1) Due to etching being directly applied to the rawmaterial, the yield rate is greatly improved. (2) No impurity issueoccurs in the manufacture process. (3) The material used has excellentstability. (4) Except structural variation at hole plating zones, thematerial of the substrate is not subjected to significant change. (5)The density of circuit traces on the substrate can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be apparent to those skilled in the art byreading the following description of preferred embodiments of thepresent invention, with reference to the attached drawings, in which:

FIG. 1 is a cross-sectional view showing a carrier board is manufacturedin the first embodiment of the present invention;

FIG. 2 is a cross-sectional view showing an upper adhesive layer isformed on the carrier board of FIG. 1;

FIG. 2A is a cross-sectional view showing an etching resisting layer isfilled in an adhesive layer opening zone of FIG. 2;

FIG. 3 is a cross-sectional view showing an upper conductor layer isformed on the upper adhesive layer and the etching resisting layer, anda lower conductor layer is formed on a bottom surface of the firstsubstrate of FIG. 2A;

FIG. 4 is a cross-sectional view showing a through hole is extendedthrough the upper conductor layer, the upper adhesive layer, the uppercircuit trace, the first substrate, and the lower conductor layer ofFIG. 3;

FIG. 5 is a cross-sectional view showing a conductive cover section isformed on a hole wall surface of the through hole, a top surface of theupper conductor layer, and a bottom surface of the lower conductor layerof FIG. 4;

FIG. 5A is a cross-sectional view showing portions of the conductivecover section and the upper conductor layer that are outside the throughhole of FIG. 5 are etched and removed;

FIG. 6 is a cross-sectional view showing the etching resisting layer ofFIG. 5A is removed;

FIGS. 7-11 are cross-sectional views showing a carrier board accordingto a second embodiment of the present invention;

FIG. 12 is a cross-sectional view showing the second embodiment of thepresent invention after being completely assembled;

FIG. 13 is another cross-sectional view showing the second embodiment ofthe present invention after being completely assembled;

FIG. 14 is a cross-sectional view, in an exploded form, showing acarrier board according to a third embodiment of the present invention;

FIG. 15 is a cross-sectional view, in an exploded form, showing acarrier board according to a fourth embodiment of the present invention;

FIG. 16 is a cross-sectional view, in an exploded form, showing acarrier board according to a fifth embodiment of the present invention;

FIG. 17 is a cross-sectional view, in an exploded form, showing acarrier board according to a sixth embodiment of the present invention;

FIG. 18 is a cross-sectional view, in an exploded form, showing acarrier board according to a seventh embodiment of the presentinvention;

FIG. 19 is a cross-sectional view showing the seventh embodiment of thepresent invention after being completely assembled;

FIG. 20 is a cross-sectional view, in an exploded form, showing acarrier board according to an eighth embodiment of the presentinvention;

FIG. 21 is a cross-sectional view, in an exploded form, showing acarrier board according to a ninth embodiment of the present invention;and

FIG. 22 is a cross-sectional view, in an exploded form, showing acarrier board according to a tenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings and in particular to FIGS. 1-6, which arecross-sectional views showing a structure of via hole of electricalcircuit board according to a first embodiment of the present inventionat different steps of manufacture process

As shown in FIG. 1, a carrier board 100 is manufactured first. In thefirst embodiment of the present invention, the carrier board 100 is aflexible circuit board, which comprises a first substrate 11. The firstsubstrate 11 has a first substrate upper surface 11 a and a firstsubstrate lower surface 11 b. The first substrate upper surface 11 aforms at least one upper circuit trace 21. The upper circuit traces 21are spaced by spacing zones 210.

After the manufacture of the carrier board 100, an upper adhesive layer31 is formed on a surface of the upper circuit trace 21 (as shown inFIG. 2). The upper adhesive layer 31 may completely cover the surface ofthe upper circuit trace 21 or locally covers partial areas of the uppercircuit trace 21. A portion of the upper circuit trace 21 that is notcovered by the upper adhesive layer 31 is defined as an upper circuittrace exposed zone 211, serving as exposed contact for a surface-mounteddevice (SMD) or finger pad conductive contacts.

As shown in FIGS. 2 and 2A, the upper adhesive layer 31 of the presentinvention is formed, in advance, with an upper adhesive layer openingzone 31 a corresponding to the upper circuit trace exposed zone 211 andan etching resisting layer 31 b is filled in the upper adhesive layeropening zone 31 a. The etching resisting layer 31 b can be made of anacid resistant material or an alkali resistant material in order toprotect the upper circuit trace exposed zone 211 from being etched in asubsequent etching process.

An upper conductor layer 41 is formed on the upper adhesive layer 31 andthe etching resisting layer 31 b. The upper conductor layer 41 shows afirst height difference h1 (as shown in FIG. 3) with respect to theupper circuit trace exposed zone 211 of the upper circuit trace 21 in avertical direction I. A lower conductor layer 42 is formed on the firstsubstrate lower surface 11 b of the first substrate 11. The lowerconductor layer 42 has a lower conductor layer bottom surface 421.

As shown in FIG. 4, at least one through hole 5 extends in the verticaldirection I through the upper conductor layer 41, the upper adhesivelayer 31, the upper circuit trace 21, the first substrate 11, and thelower conductor layer 42 and forms a hole wall surface 51. The throughhole 5 has a circumferential zone that is defined as a through holelocal zone A.

As shown in FIG. 5, after the formation of the upper conductor layer 41,the lower conductor layer 42 and the through hole 5, a conductive coversection 6 covers an upper surface of the upper conductor layer 41, thelower conductor layer bottom surface 421 of the lower conductor layer42, and the hole wall surface 51 of the through hole 5. The conductivecover section 6 may be formed with a sputtering or chemical copperprocess, and then with an electroplating process to form anelectroplated copper layer. The conductive cover section 6 comprises aconductive material selected from copper, silver, gold or a combinationthereof.

As shown in FIG. 5A, after the formation of the conductive cover section6, a portion of the conductive cover section 6 that is outside thethrough hole local zone A and a portion of the upper conductor layer 41that is outside the through hole local zone A are removed through knownetching techniques.

The upper conductor layer 41, the upper circuit trace 21, and the lowerconductor layer 42 are electrically connected to each other through theconductive cover section 6.

As shown in FIG. 6, after the portion of the conductive cover section 6formed on the upper conductor layer 41 and the portion of the upperconductor layer 41 that are outside the through hole local zone A areremoved, the etching resisting layer 31 b filled in the upper adhesivelayer opening zone 31 a is exposed. Under this condition, the etchingresisting layer 31 b can be removed to expose the upper circuit traceexposed zone 211 to serve as contact and conduction zones forsurface-mounted devices or finger pad conductive contacts.

Referring to FIGS. 7-13, which are cross-sectional views showing astructure of via hole of electrical circuit board according to a secondembodiment of the present invention at different steps of manufactureprocess, the carrier board according to the second embodiment of thepresent invention, generally designated at 200, is a double-sided board.

As shown in FIG. 7, a first double-sided board 12 has a double-sidedboard upper surface 12 a and a double-sided board lower surface 12 b,which respectively form at least one upper circuit trace 21 and at leastone lower circuit trace 22. The upper circuit traces 21 are spaced byspacing zones 210 and the lower circuit traces 22 are spaced by spacingzones 220. The upper circuit trace 21 comprises at least one uppercircuit trace exposed zone 211, and the lower circuit trace 22selectively comprises at least one lower circuit trace exposed zone 221.

As shown in FIGS. 8 and 9, an upper adhesive layer 31 is formed on asurface of the upper circuit trace 21. A lower adhesive layer 32 isformed on a surface of the lower circuit trace 22. An upper conductorlayer 41 is formed on a surface of the upper adhesive layer 31. Theupper conductor layer 41 shows a first height difference h1 with respectto the upper circuit trace exposed zone 211 of the upper circuit trace21 in a vertical direction I.

A lower conductor layer 42 is formed on a surface of the lower adhesivelayer 32. The lower conductor layer 42 shows a second height differenceh2 with respect to the lower circuit trace exposed zone 221 of the lowercircuit trace 22 in the vertical direction I.

As shown in FIG. 10, at least one through hole 5 extends in the verticaldirection I through the upper conductor layer 41, the upper adhesivelayer 31, the upper circuit trace 21, the first double-sided board 12,the lower circuit trace 22, the lower adhesive layer 32, and the lowerconductor layer 42, and forms a hole wall surface 51.

As shown in FIG. 11, a conductive cover section 6 covers an uppersurface of the upper conductor layer 41, a lower surface of the lowerconductor layer 42, and the hole wall surface 51 of the through hole 5.

As shown in FIG. 12, the portion of the conductive cover section 6 thatis other than that adjacent the through hole 5 and the portion of theupper conductor layer 41 that is other than that adjacent the throughhole 5 are removed through known etching techniques or are partlypreserved.

As shown in FIG. 13, the portion of the conductive cover section 6 thatis other than that adjacent the through hole 5 and the portion of thelower conductor layer 42 that is other than that adjacent the throughhole 5 are removed through known etching techniques or are partlypreserved.

FIG. 14 is a cross-sectional view showing a carrier board according to athird embodiment of the present invention, generally designated at 300,which comprises two single-sided boards. As shown in the drawing, thecarrier board comprises at least one first substrate 11, which has afirst substrate upper surface 11 a and a first substrate lower surface11 b, and at least one upper circuit trace 21 is formed on the firstsubstrate upper surface 11 a. At least one second substrate 13 has asecond substrate upper surface 13 a and a second substrate lower surface13 b, and the second substrate upper surface 13 a is bonded by a bondinglayer 71 to the first substrate lower surface 11 b of the firstsubstrate 11. At least one lower circuit trace 22 is formed on thesecond substrate lower surface 13 b. The bonding layer 71 shows materialproperties of adhesion and insulation. The carrier board 300 of thethird embodiment can replace the carrier board 100 of the firstembodiment and the manufacture process illustrated in FIGS. 2-6 isapplicable to the carrier board of the third embodiment to form astructure of electrical circuit board via hole that is composed of twosingle-sided boards.

FIG. 15 is a cross-sectional view showing a carrier board according to afourth embodiment of the present invention, generally designated at 400,which comprises three single-sided boards. The general structure of thefourth embodiment is similar to that of FIG. 14, but at least one thirdsubstrate 14 and bonding layers 71, 72 are arranged between the secondsubstrate upper surface 13 a of the second substrate 13 and the firstsubstrate lower surface 11 b of the first substrate 11. The thirdsubstrate 14 has a surface on which at least one intermediate circuittrace 23 is formed.

FIG. 16 is a cross-sectional view showing a carrier board according to afifth embodiment of the present invention, generally designated at 500,which comprises two single-sided boards and one double-sided board. Thecarrier board of the fifth embodiment comprises a first substrate 11,which has a first substrate upper surface 11 a and a first substratelower surface 11 b, and at least one upper circuit trace 21 is formed onthe first substrate upper surface 11 a. A second substrate 13 has asecond substrate upper surface 13 a and a second substrate lower surface13 b, and at least one lower circuit trace 22 is formed on the secondsubstrate lower surface 13 b.

At least one first double-sided board 12 is arranged between the secondsubstrate upper surface 13 a of the second substrate 13 and the firstsubstrate lower surface 11 b of the first substrate 11. The firstdouble-sided board 12 has a double-sided board upper surface 12 a and adouble-sided board lower surface 12 b, each of which forms at least oneintermediate circuit trace 23 a, 23 b. The double-sided board uppersurface 12 a is bonded by a bonding layer 71 to the first substratelower surface 11 b of the first substrate 11 and the double-sided boardlower surface 12 b is bonded by a bonding layer 72 to the secondsubstrate upper surface 13 a of the second substrate 13.

FIG. 17 is cross-sectional view showing a carrier board according to asixth embodiment of the present invention, generally designated at 600,which comprises one single-sided board and one double-sided board. Thecarrier board of the sixth embodiment comprises a first substrate 11,which has a first substrate upper surface 11 a and a first substratelower surface 11 b, and at least one upper circuit trace 21 is formed onthe first substrate upper surface 11 a. At least one first double-sidedboard 12 has a double-sided board upper surface 12 a and a double-sidedboard lower surface 12 b. The double-sided board upper surface 12 a isbonded by a bonding layer 71 to the first substrate lower surface 11 bof the first substrate 11. At least one lower circuit trace 22 is formedon the double-sided board lower surface 12 b. At least one intermediatecircuit trace 23 is formed on the double-sided board upper surface 12 aof the first double-sided board 12.

FIG. 18 is a cross-sectional view showing a carrier board according to aseventh embodiment of the present invention, generally designated at700, which comprises two double-sided boards and FIG. 19 is across-sectional view showing the seventh embodiment after beingcompletely assembled. The carrier board 700 comprises a firstdouble-sided board 12, which has a double-sided board upper surface 12 aand a double-sided board lower surface 12 b, and at least one uppercircuit trace 21 is formed on the double-sided board upper surface 12 a.At least one second double-sided board 15 has a double-sided board uppersurface 15 a and a double-sided board lower surface 15 b. Thedouble-sided board upper surface 15 a is bonded by a bonding layer 71 tothe double-sided board lower surface 12 b of the first double-sidedboard 12. At least one lower circuit trace 22 is formed on thedouble-sided board lower surface 15 b of the second double-sided board15. At least one first double-sided board intermediate circuit trace 23c is formed on the double-sided board lower surface 12 b of the firstdouble-sided board 12. At least one second double-sided boardintermediate circuit trace 23 d is formed on the double-sided boardupper surface 15 a of the second double-sided board 15.

Referring to FIG. 19, after the assembling, an upper adhesive layer 31is formed on at least a partial area of the upper circuit trace 21 ofthe first double-sided board 12 and the portion of the upper circuittrace 21 that is not covered by the upper adhesive layer 31 is definedas an upper circuit trace exposed zone 211. An upper conductor layer 41is formed on an upper surface of the upper adhesive layer 31. The upperconductor layer 41 shows a first height difference h1 with respect tothe upper circuit trace exposed zone 211 in a vertical direction I.

A lower adhesive layer 32 is formed on at least a partial area of thelower circuit trace 22 of the second double-sided board 15 and theportion of the lower circuit trace 22 that is no covered by the loweradhesive layer 32 is defined as a lower circuit trace exposed zone 221.A lower conductor layer 42 is formed on a lower surface of the loweradhesive layer 32. The lower conductor layer 42 shows a second heightdifference h2 with respect to the lower circuit trace exposed zone 221in the vertical direction I.

At least one through hole 5 extends in the vertical direction I throughthe upper conductor layer 41, the upper adhesive layer 31, the uppercircuit trace 21, the first double-sided board 12, the firstdouble-sided board intermediate circuit trace 23 c, the bonding layer71, the second double-sided board intermediate circuit trace 23 d, thesecond double-sided board 15, the lower circuit trace 22, the loweradhesive layer 32, and the lower conductor layer 42, and forms a holewall surface 51. A conductive cover section 6 covers the hole wallsurface 51 of the through hole 5, a partial area of the upper conductorlayer 41 of the first double-sided board 12 that is adjacent to thethrough hole 5, and a partial area of the lower conductor layer 42 ofthe second double-sided board 15 that is adjacent to the through hole 5.

In a practical application, the through hole 5 can be selectively andelectrically connected to the upper circuit trace 21, the lower circuittrace 22, the first double-sided board intermediate circuit trace 23 c,the second double-sided board intermediate circuit trace 23 d, asdesired.

FIG. 20 is cross-sectional view showing a carrier board according to aneighth embodiment of the present invention, generally designated at 800,which comprises one single-sided board and one double-sided board. Asshown in the drawing, the carrier board of the eighth embodimentcomprises at least one first substrate 11 and one first double-sidedboard 12. The first double-sided board 12 comprises a buried hole 8. Theburied hole 8 has a structure similar to the structure of the throughhole 5 shown in FIG. 13, but the buried hole 8 is pre-formed before thefirst substrate 11 and the first double-sided board 12 are bonded. Thefirst double-sided board 12 has an upper surface forming an uppercircuit trace that serves as an intermediate circuit trace 24. The firstdouble-sided board 12 has a lower surface forming at least one lowercircuit trace 22. The first substrate 11 has an upper surface 11 aforming at least one upper circuit trace 21. The first double-sidedboard 12 and the first substrate 11 are bonded to each other by abonding layer 73.

After the first substrate 11 and the first double-sided board 12 arebonded together by the bonding layer 73, a manufacture process as whatdescried above is performed, for making a through hole, at a locationshifted from the buried hole 8. This completes a structure ofthree-layered electrical circuit board comprising a buried hole and anintermediate circuit trace layer to serve as the carrier board accordingto the present invention.

In the instant embodiment, a single-sided board is bonded by a bondinglayer 73 to a double-sided board in which a buried hole 8 is formed inadvance to form a carrier board 800. The carrier board 800 may thenreplace the carrier board 100 of the first embodiment to subject to themanufacture process illustrated in FIGS. 2-6 at a location that isshifted from the buried hole 8 of the first double-sided board 12. Thiscompletes a structure of via hole of electrical circuit board thatcomprises a buried hole and an intermediate circuit trace layer.

FIG. 21 is a cross-sectional view showing a carrier board according to aninth embodiment of the present invention, generally designated at 900,which comprises two double-sided boards. As shown in the drawing, thecarrier board of the ninth embodiment comprises at least twodouble-sided boards 12, 15, and the two double-sided boards each form aburied hole 8 a, 8 b in advance. The first double-sided board 12 has adouble-sided board upper surface 12 a that forms at least oneintermediate circuit trace 24. The double-sided board has a double-sidedboard lower surface 12 b that forms at least one lower circuit trace 22.The second double-sided board 15 has a double-sided board lower surface15 b that forms at least one intermediate circuit trace 25 and adouble-sided board upper surface 15 a that forms at least one uppercircuit trace 21. The two double-sided boards 12, 15 are bonded to eachother by a bonding layer 74.

After the two double-sided boards 12, 15 are bonded together by thebonding layer 74, the manufacture process for through hole discussedabove can then be carried out in order to complete a structure offour-layered electrical circuit board that has buried holes andintermediate circuit trace layers to serve as a carrier board of thepresent invention. In the instant embodiment, two double-sided boards12, 15 that form buried holes in advance are bonded together by abonding layer 74 to form a carrier board 900, and then, the carrierboard 900 may replace the carrier board 100 of the first embodiment tosubject to the manufacture process illustrated in FIGS. 2-6 by avoidingthe locations of the buried holes so as to complete a structure of viahole of electrical circuit board that comprise buried holes andintermediate circuit trace layers.

FIG. 22 is cross-sectional view showing a carrier board according to atenth embodiment of the present invention, generally designated at 901,which comprises one double-sided board and two single-sided boards. Asshown in the drawing, the carrier board of the tenth embodimentcomprises at least one first double-sided board 12, which comprise apre-formed buried hole 8. The first double-sided board 12 has adouble-sided board upper surface 12 a and a double-sided board lowersurface 12 b, which respectively form at least one intermediate circuittrace 24, 26 and are respectively bonded by bonding layers 75, 76 to afirst substrate 11 and a second substrate 13. The first substrate 11 andthe second substrate 13 are both single-sided boards. The firstsubstrate 11 has an upper surface 11 a forming at least one uppercircuit trace 21, and the second substrate 13 has a lower surface 13 bforming at least one lower circuit trace 22.

After the first double-sided board 12 and the first and secondsubstrates 11, 13 are bonded to each other by the bonding layers 75, 76,the manufacture process illustrated in FIGS. 2-6 is performed at alocation avoiding the buried hole 8 of the first double-sided board 12in order to complete a structure of four-layered electrical circuitboard comprising a buried hole and intermediate circuit trace layers toserve as the carrier board according to the present invention.

It is appreciated from the above embodiments that the present inventioncombines one or more single-sided boards and double-sided boards ormulti-layered boards to form various structures of carrier board,wherein the single-sided boards, the double-sided boards, and themulti-layered boards can be circuit boards of different properties, suchas flexible circuit boards, rigid circuit boards, and composite boardsof flexible and rigid boards. And, various embodiments can be made bycombining the structure of via hole and the manufacture processaccording to the present invention.

Although the present invention has been described with reference to thepreferred embodiments thereof, it is apparent to those skilled in theart that a variety of modifications and changes may be made withoutdeparting from the scope of the present invention which is intended tobe defined by the appended claims.

What is claimed is:
 1. A method for manufacturing an electrical circuitboard, comprising the following steps: (a) manufacturing a carrierboard, the carrier board being a flexible circuit board, the carrierboard comprising a first substrate, which has a substrate upper surfaceand a substrate lower surface, the substrate upper surface comprising atleast one upper circuit trace; (b) forming an upper adhesive layer onthe upper circuit trace; (c) forming an upper adhesive layer openingzone in a portion of the upper adhesive layer that exposes a portion ofthe upper circuit trace thus forming an upper circuit trace exposedzone; (d) filling an etching resisting layer in the upper adhesive layeropening zone; (e) forming an upper conductor layer on the upper adhesivelayer and the etching resisting layer, the upper conductor layer showinga first height difference with respect to the upper circuit traceexposed zone of the upper circuit trace in a vertical direction; (f)forming a lower conductor layer on the substrate lower surface of thecarrier board, the lower conductor layer having a lower conductor layerbottom surface; (g) forming at least one through hole, which extends inthe vertical direction through the upper conductor layer, the upperadhesive layer, the upper circuit trace, the first substrate and thelower conductor layer and forms a hole wall surface, the through holehaving a circumferential zone defining a through hole local zone; (h)forming a conductive cover section to cover the hole wall surface of thethrough hole, the upper conductor layer, and the lower conductor layerbottom surface of the lower conductor layer so as to have the upperconductor layer, the upper circuit trace, and the lower conductor layerto electrically connect with each other through the conductive coversection; and (i) removing a portion of the conductive cover section thatis outside the through hole local zone and a portion of the upperconductor layer that is outside the through hole local zone.
 2. Themethod as claimed in claim 1, wherein a conductive material used by theconductive cover section is selected from one of copper, silver, andgold or a combination thereof.
 3. The method as claimed in claim 1,wherein the etching resisting layers are made of one of an acidresistant material and an alkali resistant material.
 4. The method asclaimed in claim 1, wherein after step (i), removing the etchingresisting layer from the upper adhesive layer opening zone of the upperadhesive layer.